Transparent composite panel

ABSTRACT

A transparent nanofiber composite panel that includes a plurality of transparent nanofibers integrated in random orientations within a transparent matrix is provided. The transparent nanofibers have a diameter that is less than the wavelength of visible light. The extremely small diameter of the transparent nanofibers allows the transparent panel to be substantially insensitive to an RI ‘mismatch’ between the transparent nanofibers and the transparent matrix. Additionally, due to random orientation of the transparent nanofibers within the transparent matrix the transparent nanofiber composite panel possesses substantially isotropic material properties such that the transparent nanofiber composite panel can be incorporated as a structural, load bearing, component of a larger structure.

FIELD OF THE INVENTION

The present invention relates to composite transparencies and moreparticularly to transparent composites utilized to provide transparentstructural panels that can be incorporated into the structure of amobile platform.

BACKGROUND OF THE INVENTION

Composite transparencies have many applications in many devices andstructures. For example, composite transparencies can be utilized ineyeglasses, high security display cases, high-rise building windows andfighter jet cockpit canopies. In a particular instance, compositetransparencies can be utilized to construct windows of a mobile platformsuch as an aircraft, train, bus, tank or ship. Generally, mobileplatform windows formed of known transparent materials are not suitablefor use as structural component of the mobile platform. In manyinstances, windows in many commercial mobile platforms are relativelysmall in size, due, at least in part, to the limited capabilities ofcurrent transparent window materials to carry a load and also due to theheavy and complex support structure needed to carry mobile platformfuselage loads around the window cutout in the absence of a load bearingtransparency.

Typically, these transparent window materials consist of a transparentpolymer that exhibits such useful qualities as good transparency andeasy formation of complex shapes. However, these polymer windowstypically have a limited strength capability, tend to be notchsensitive, and craze, i.e. form nuisance cracks, over time at very lowstress levels. Moreover, these windows generally require a heavy supportstructure in order to support the window within the fuselage structureof the mobile platform. Each component of such a support structure isdesigned to strengthen panels of the fuselage that surround and supporteach window. However, each component increases the cost and weight ofthe completed window assembly, thereby providing an incentive to keepsome mobile platform windows relatively small.

In at least some known instances, fiber reinforced transparentcomposites have been utilized in constructing mobile platform windowsthat are lighter and stronger than the transparent polymer windowstypically used. Such composite windows typically include a transparentfiber integrated within a transparent polymer matrix, e.g. an epoxyresin. To provide high quality transparent properties of suchcomposites, the refraction index (RI) of the transparent fiber mustsubstantially match that of the polymer matrix to a third decimal place.While such RI matching is straightforward, problems arise due to a‘mismatch’ in the RI's as a function of temperature change. That is, asthe environmental temperature to which the transparent composite isexposed changes, the RI of the polymer matrix and/or the RI of the fiberwill change such that there is a ‘mismatch’ between the RI's of thematrix and the fiber. Typically, the RI changes significantly for thepolymer matrix but is relatively constant for the fiber. Therefore,changes in the environmental temperature, either increases and/ordecreases, can cause a ‘mismatch’ of RI's of the matrix and the fiber. Asignificant ‘mismatch’, e.g. greater than 0.01, between the RI of thematrix and the RI of the fiber causes clouding of the transparentcomposite.

Accordingly, the present invention seeks to provide the art with astrong composite transparency that can provide excellent structuralstrength and does not suffer from opacity at extreme temperatures. Thepresent invention is focused on use with an aircraft window, however itis applicable to any transparency where high strength and lightweightconstruction are of paramount importance.

SUMMARY OF THE INVENTION

A transparent nanofiber composite panel is provided in accordance with apreferred embodiment of the present invention. The transparent nanofibercomposite panel includes a plurality of transparent nanofibersintegrated in random orientations within a transparent matrix. Thetransparent nanofibers have a diameter that is less than the wavelengthof visible light. In a preferred exemplary embodiment, the transparentnanofibers are constructed of glass. Alternatively, the transparentnanofibers can be constructed of any other suitable transparent materialhaving high strength properties, for example, silicon dioxide, graphiteor a transparent polymer such as nylon or polycarbonate.

In a preferred form, the transparent matrix is formed from a transparentepoxy resin. The high transmittance of the transparent nanofibersresulting from having a diameter less than the wavelength of visiblelight permits variations in the refraction index (RI) of the matrix thatmay occur due to extreme temperatures, without affecting thetranslucency of the transparent nanofiber composite panel. Morespecifically, the extremely small diameter of the transparent nanofibersallows the transparent panel to be substantially insensitive to an RI‘mismatch’ between the transparent nanofibers and the transparentmatrix.

Due to the random orientation of the transparent nanofibers within thetransparent matrix, the transparent nanofiber composite panel comprisessubstantially isotropic material properties. For example, thetransparent nanofiber composite panel possesses approximately equalstrength in all directions. Therefore, the transparent nanofibercomposite panel can be incorporated as a structural, load bearing,component of a larger structure, e.g. a mobile platform fuselage.

The features, functions, and advantages can be achieved independently invarious embodiments of the present inventions or may be combined in yetother embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is an illustration of an exemplary mobile platform including atransparent nanofiber composite panel according to the principles of thepresent invention;

FIG. 2 is a sectional view of the transparent nanofiber composite panelshown in FIG. 1;

FIG. 3 is an exemplary schematic view of a method of forming transparentnanofibers for use with the transparent nanofiber composite panel shownin FIG. 1;

FIG. 4A is a schematic view of an injection mold used to construct thetransparent nanofiber composite panel, shown in FIG. 1, in accordancewith a preferred embodiment of the present invention; and

FIG. 4B is a schematic view of a nanofiber pre-impregnated tape used toconstruct the transparent nanofiber composite panel, shown in FIG. 1, inaccordance with another preferred embodiment of the present invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

With reference to FIG. 1, a transparent nanofiber composite panel 10constructed according to the principles of the present invention isshown in operative association with a mobile platform 12. Moreparticularly, the transparent nanofiber composite panel 10 is an opticalquality fiber reinforced transparency having high structural strengthproperties. Although the mobile platform 12 is shown as an aircraft, themobile platform 12 could also be represented in the form of other mobileplatforms, such as a ship, a train, a bus or an automobile.Additionally, although the present invention will be described below asparticularly applicable for use in association with mobile platforms,the invention should not be so limited in application. It is envisionedthat the invention is equally applicable to aircraft, trains, buses,tanks, ships, buildings, or any application where a compositetransparency having high strength and lightweight construction is ofparamount importance.

In the particular example provided, the transparent nanofiber compositepanel 10 is shown as a window of the mobile platform 12. It should beappreciated, however, that the transparent nanofiber composite panel 10may be used in any portion of the mobile platform 12 and may include thecockpit window or a door window. Moreover, the transparent nanofibercomposite panel 10 may be used in any number of environments notstrictly limited to conventional “windows”. For example, skylights,running light covers, satellite dome covers, view ports on underseawatercraft, and various other environments may employ the transparentnanofiber composite panel 10 of the present invention.

The mobile platform 12 generally includes a fuselage 14 that surroundsthe transparent nanofiber composite panel 10. A traditional prior artside window is shown in FIG. 1 in phantom lines and is generallyindicated by reference numeral 16. As is apparent, the transparentnanofiber composite panel 10 has a larger field of view than thetraditional prior art side window 16. This is due, in part, to thegreater strength and load carrying capability of the transparentnanofiber composite panel 10, as further described below.

Turning to FIG. 2, a portion of the transparent nanofiber compositepanel 10 is illustrated. The transparent nanofiber composite panel 10generally includes a plurality of transparent nanofibers 18 integratedwithin a transparent matrix 20. The transparent nanofibers 18 have adiameter, “d”. In a preferred embodiment the diameter d of thetransparent nanofibers 18 is less than the wavelength of visible light,i.e., less than approximately 400 to 600 nm. Preferably, the transparentnanofibers 18 have a diameter d of between approximately 10 to 400 nm.In the particular example provided, the transparent nanofibers 18 areconstructed of glass. However, the transparent nanofibers 18 can beconstructed of any other suitable transparent material having highstrength properties as described herein; for example, silicon dioxide,graphite or a transparent polymer such as nylon or polycarbonate.

In a preferred form, the matrix 20 is formed from a transparent epoxyresin. The epoxy resin is selected based on transparency, strength, andrefractive index (RI). Preferably, the RI of the matrix 20 issubstantially similar to the RI of the transparent nanofibers 18.However, the high transmittance of the transparent nanofibers 18 of thepresent invention, as described below, permits variations in the RI ofthe matrix 20 that may occur due to extreme temperatures, withoutaffecting the translucency of the transparent nanofiber composite panel10.

In accordance with a preferred implementation of the present invention,due to the diameter d being less than the wavelength of visible light,the transparent nanofibers 18 permit transmittance of light on the orderof 90%. Moreover, because the transmittance of the transparentnanofibers 18 is very high, it is possible to allow dissimilar RIsbetween the transparent nanofibers 18 and the transparent matrix 20without the transparent nanofiber composite panel 10 becoming opaque.Additionally, as the diameter of the transparent nanofibers 18decreases, fiber strength increases due to a reduction in surfacedefects. This is especially true of glass nanofibers, which have beenshown to exhibit linearly increasing tensile strength up to 1×10⁶ PSIfor fiber diameters of approximately 1000 nm.

Preferably the transparent nanofibers 18 are distributed within thematrix 20 at approximately 10% to 60% by volume. Due to the high tensilestrength of the transparent nanofibers 18, as the diameter of thetransparent nanofibers 18 decreases, the concentration of transparentnanofibers 18 integrated with the transparent matrix 20 can decreasewithout sacrificing the structural strength properties of thetransparent nanofiber composite panel 10.

Moreover, due to the high tensile strength of the transparent nanofibers18, the transparent nanofibers 18 can be distributed within the matrix20 at random orientations without sacrificing the structural strengthproperties of the transparent nanofiber composite panel 10. That is, dueto the high tensile strength of the small diameter transparentnanofibers 18 sufficient strength will remain in the transparentnanofiber composite panel 10 without integrating the transparentnanofibers 18 within the transparent matrix 20 in a particularorientation. Furthermore, the random orientation of the transparentnanofibers 18 within the transparent matrix 20 provides the transparentnanofiber composite panel 10 with quasi-isotropic material properties,e.g. approximately equal strength in all directions. Therefore, thetransparent nanofiber composite panel 10 can be incorporated as astructural, load bearing, component of the mobile platform fuselage 14.

With reference to FIG. 3, the transparent nanofibers 18 are preferablyproduced by spinning the material through a powerful electric field,known in the art as “electrospinning”, though various other methods maybe employed. A polymer melt 22, glass in the particular exampleprovided, is pumped from a source 24 through a feed line 26 to aspinneret 28. The spinneret 28 extends between a top plate 30 and abottom plate 32. The top plate 30 is charged via a power source 34. Anelectric field is thereby formed that in turn electrostatically chargesthe melt 22 as it leaves the spinneret 28. As the polymer melt 22 isspun out from the spinneret 28, the electric field draws out the melt 22into nanofibers that may then be collected on the bottom plate 32.

In a preferred implementation, the transparent nanofibers 18 areintegrated with the transparent matrix 20 utilizing an injection moldingprocess as illustrated in FIG. 4A. A mold 38 generally includes moldhalves 40 that combine to form a designated shape, such as, for example,a window shape. Epoxy resin 42 and transparent nanofibers 18 are theninjected into the mold 38. Once the epoxy resin 42 has set or cured, thetransparent nanofiber composite panel 10 may then be removed from themold 38. Since the transparent nanofibers 18 may be randomly orientedwithin the mold 38, it is possible for the mold 38 to take on any shapedesired, thereby allowing windows that have complex surfaces.

Turning to FIG. 4B, in an alternative preferred embodiment, thetransparent nanofibers 18 are used to form a reinforced pre-impregnatedtape 36. For example, the transparent nanofibers 18 may be arranged in aresin that, after solidification, forms the transparent matrix 20 in theform of strips of pre-impregnated tape 36. Successive layers of thepre-impregnated tape 36 may then be laminated to form the transparentnanofiber composite panel 10. Due to the random orientation of thetransparent nanofibers 18 on the pre-impregnated tape 36, thepre-impregnated tape 36 need not be aligned in any particular mannerwhen laminated with layers of other pre-impregnated tape 36 to form thetransparent nanofiber composite panel 10.

In yet another preferred embodiment, the transparent nanofibers 18 arewoven into a ‘cloth’. The transparent nanofiber ‘cloth’ is then exposedto the transparent matrix 20, such that the transparent matrix 20penetrates the transparent nanofiber ‘cloth’.

By employing transparent nanofibers integrated within a transparentmatrix, the transparent nanofiber composite panel 10 is substantiallyinsensitive to RI ‘mismatch’, e.g. ‘mismatch’ caused by changes in theenvironmental temperature. That is, the transparent nanofiber compositepanel 10 will maintain a high level of transparency, e.g. 90%, over awide range of temperature. In an exemplary embodiment the transparentnanofiber composite panel 10 will maintain a high level of transparencyat temperatures ranging between approximately (−60)° F. andapproximately 400° F. Moreover, the transparent nanofiber compositepanel 10 is substantially stronger and is capable of use as a loadbearing structural component of the mobile platform 12. For example, inthe case where the transparent nanofiber composite panel 10 is a windowin a mobile platform fuselage, a load can be transferred across thewindow so that additional fuselage structure does not need to beincorporated around the window. Preferably, the transparent nanofibers18 are constructed of glass to thereby provide significant tensilestrength and allow lower concentration of the transparent nanofibers 18within the transparent matrix 20. The lower concentration providesfurther increases in transmittance and decreases in optical distortionof light through the transparent nanofiber composite panel 10. Ifpolymer material is used to construct the transparent nanofibers 18, itis preferable to select a polymer material with a RI and an indexvariation substantially similar to the RI and index variation of thetransparent matrix 20.

Furthermore, the transparent nanofiber composite panel 10 constructedwith the transparent nanofibers 18 randomly oriented within thetransparent matrix 20, as described above, is not limited tounidirectional strength. Thus, the transparent nanofiber composite panel10 will have quasi-isotropic material properties.

While various preferred embodiments have been described, those skilledin the art will recognize modifications or variations, which might bemade without departing from the inventive concept. The examplesillustrate the invention and are not intended to limit it. Therefore,the description and claims should be interpreted liberally with onlysuch limitation as is necessary in view of the pertinent prior art.

1. A transparent panel comprising: a transparent matrix; and a pluralityof transparent nanofibers integrated within the transparent matrix, thetransparent nanofibers having a diameter less than the wavelength ofvisible light.
 2. The transparent panel of claim 1, wherein thetransparent nanofibers have a diameter between approximately 10 nm and400 nm.
 3. The transparent panel of claim 1, wherein the transparentnanofibers comprise glass transparent nanofibers.
 4. The transparentpanel of claim 1, wherein the transparent nanofibers compriseapproximately 10% to 60% of the transparent panel by volume.
 5. Thetransparent panel of claim 1, wherein an index of refraction of thetransparent nanofibers approximately equals an index of refraction (RI)of the transparent matrix.
 6. The transparent panel of claim 1, whereinthe transparent nanofibers are integrated within the transparent matrixto form a non-woven transparent nanofiber mat tape used to construct thetransparent panel.
 7. The transparent panel of claim 1, wherein thetransparent nanofibers form a mat cloth that is integrated within thetransparent matrix to form the transparent panel.
 8. The transparentpanel of claim 1, wherein the transparent nanofibers and the transparentmatrix are injected into a mold to form the transparent panel.
 9. Thetransparent panel of claim 1, wherein the transparent matrix comprisesan epoxy resin.
 10. The transparent panel of claim 1, wherein thetransparent nanofibers comprise a polymer.
 11. The transparent panel ofclaim 1, wherein the transparent nanofibers are integrated within thetransparent matrix in a random orientation to provide a structural loadbearing transparent panel comprising substantially isotropic strengthsuch that a load can be transferred across the transparent panel in anydirection.
 12. The transparent panel of claim 11, wherein the structuralload bearing transparent panel is adapted to be incorporated as atransparent structural, load bearing member within a fuselage of amobile platform.
 13. The transparent panel of claim 1, wherein thetransparent panel comprises an optical quality transparent panel adaptedto permit approximately 90% transmittance of light.
 14. The transparentpanel of claim 1, wherein the transparent panel is adapted to maintainan approximately constant level of transparency at temperatures rangingbetween approximately (−60)° F. and approximately 400° F.
 15. Thetransparent panel of claim 1, wherein the transparent panel is adaptedto be substantially insensitive to an RI ‘mismatch’ between thetransparent nanofibers and the transparent matrix
 16. A method forproviding a structural load bearing transparent panel havingsubstantially isotropic material properties over a wide range oftemperatures, the method comprising: providing a transparent matrix;providing a plurality of transparent nanofibers having a diameter lessthan the wavelength of visible light; integrating the transparentnanofibers within a transparent matrix to form the transparent panelcomprising substantially isotropic strength such that a load can betransferred across the transparent panel in any direction and adapted tobe substantially insensitive to a difference between a refractive index(RI) of the transparent matrix and a RI of the transparent nanofibers.17. The method of claim 16, wherein integrating the transparentnanofibers within a transparent matrix comprises integrating thetransparent nanofibers within a transparent matrix in a randomorientation such that the transparent panel comprises substantiallyisotropic material properties.
 18. The method of claim 16, whereinproviding the plurality of transparent nanofibers comprises providingthe transparent nanofibers having a diameter between approximately 10 nmand 400 nm.
 19. The method of claim 16, wherein providing the pluralityof transparent nanofibers comprises providing glass nanofibers.
 20. Themethod of claim 16, wherein integrating the transparent nanofiberswithin a transparent matrix comprises integrating the transparentnanofibers such that the transparent nanofibers comprise approximately10% to 60% of the transparent panel by volume.
 21. The method of claim16, wherein providing the plurality of transparent nanofibers comprisesproviding the nanofibers having a RI approximately equal to RI of thetransparent matrix.
 22. The method of claim 16, wherein integrating thetransparent nanofibers within a transparent matrix comprises:integrating the transparent nanofibers within the transparent matrix toform a non-woven transparent nanofiber mat tape; and bonding together aplurality of pieces of the transparent nanofiber mat tape to constructthe transparent panel.
 23. The method of claim 16, wherein integratingthe transparent nanofibers within a transparent matrix comprises:forming a mat cloth from the transparent nanofibers; and integratingwithin the transparent matrix with the mat cloth to form the transparentpanel.
 24. The method of claim 16, wherein integrating the transparentnanofibers within a transparent matrix comprises injecting thetransparent nanofibers and the transparent matrix into a mold to formthe transparent panel.
 25. The method of claim 16, wherein providing thetransparent matrix comprises providing an epoxy resin to be integratedwith the transparent nanofibers.
 26. The transparent panel of claim 16,wherein providing the transparent nanofibers comprises providing apolymer to be integrated with the transparent matrix.
 27. The method ofclaim 16, wherein the method further comprises incorporating thetransparent panel within a fuselage of a mobile platform as atransparent structural, load bearing member.
 28. The method of claim 16,wherein integrating the transparent nanofibers within a transparentmatrix comprises integrating the transparent nanofibers within thetransparent matrix such that the transparent panel permits approximately90% transmittance of light.
 29. The method of claim 16, whereinintegrating the transparent nanofibers within a transparent matrixcomprises integrating the transparent nanofibers within the transparentmatrix such that such that the transparent panel is maintains anapproximately constant level of transparency at temperatures rangingbetween approximately (−60)° F. and approximately 400° F.
 30. Ananofiber composite panel for use in the structure of a mobile platform,said panel comprising: a transparent epoxy resin; and a plurality oftransparent nanofibers integrated within the transparent epoxy resin ina random orientation to provide a transparent panel having substantiallyisotropic strength such that a load can be transferred across thetransparent panel in any direction; wherein the transparent nanofiberscomprise: a diameter having a length less than the wavelength of visiblelight such that the transparent panel is substantially insensitive to adifference between a refractive index (RI) of the transparent epoxyresin and a RI of the transparent nanofibers.
 31. The panel of claim 30,wherein the length of the diameter of the transparent nanofibers isbetween approximately 10 nm and 400 nm.
 32. The panel of claim 30,wherein the transparent nanofibers comprise glass nanofibers.
 33. Thepanel of claim 30, wherein the transparent nanofibers comprise polymernanofibers.
 34. The panel of claim 30, wherein the transparentnanofibers comprise approximately 10% to 60% of the transparent panel byvolume.
 35. The panel of claim 30, wherein an index of refraction of thetransparent nanofibers approximately equals an index of refraction (RI)of the transparent epoxy resin.
 36. The panel of claim 30, wherein thetransparent nanofibers are integrated within the transparent epoxy resinto form a non-woven transparent nanofiber mat tape used to construct thetransparent panel.
 37. The panel of claim 30, wherein the transparentnanofibers form a mat cloth that is integrated within the transparentepoxy resin to form the transparent panel.
 38. The panel of claim 30,wherein the transparent nanofibers and the transparent epoxy resin areinjected into a mold to form the transparent panel.
 39. The panel ofclaim 11, wherein the transparent panel is adapted to be incorporated asa transparent structural, load bearing member within a fuselage of amobile platform.
 40. The panel of claim 30, wherein the transparentpanel comprises an optical quality transparent panel adapted to permitapproximately 90% transmittance of light.